IOS. 11 or 12?

iOS is for iPhones, iPads and iPods. MacOS is for MacBooks, iMacs and the like.

When you click the black Apple at the top left corner of your screen and choose 'about this Mac', you'll see what macOS is installed on the computer.

You can click on the App Store (the white A in the blue circle) and then tap on 'updates' to see what macOS updates might be available for your McBook.

iOS is the operating system for mobile devices, such as the iPhone, iPad. A MacBook Air would be using OS X, a different thing. If you wish to know something about iOS, then is your profile correct that you have an iPhone 6 Plus? If you are trying to update iOS on the iPhone 6, the current iOS is 12.0.1. If you are trying to update via the computer, see this for help in determining the latest version of iTunes, 12.9, which is required for updating to iOS 12.x. Update your iPhone, iPad, or iPod touch - Apple Support

If you are looking for assistance with the OS for the MacBook Air, then describe your issue and we can have the thread moved to a more appropriate forum.